A cathode-ray tube (CRT) display device comprises a CRT, a support structure, such as a CRT enclosure or chassis, for the CRT, and a deflection yoke. The CRT has a faceplate that is usually of generally rectangular form and has an outer surface that is presented towards the viewer of the CRT and an inner surface that is presented towards an electron gun structure mounted in the neck of the CRT. The faceplate has a layer of phosphor material over its inner surface. In the case of a conventional shadowmask color CRT, the layer of phosphor material comprises three phosphors, which emit the three primary colors respectively. The three phosphors are deposited over the inner surface of the faceplate in groups or triads each comprising one dot or stripe of each phosphor color. The triads are uniformly distributed over the inner surface of the faceplate, being arranged in parallel rows that are on equally-spaced centerlines. When the deflection yoke is appropriately driven, the rows of triads are scanned successively by the electron beams generated by the electron gun structure. The array of parallel lines traced out on the faceplate by the electron beams is commonly referred to as the raster of the CRT. The orientation of the raster about the central axis of the CRT is determined by the positioning of the deflection yoke on the neck of the CRT.
The rows of phosphor triads are deposited on the inner surface of the faceplate by screen printing, and the orientation of the printing screen is set by reference to three alignment projections at the exterior of the faceplate. The alignment projections are also used to establish the orientation of the shadowmask relative to the faceplate. It is conventional for the shadowmask of an in-line CRT to include four apertures that result in two pairs of triads outside the central display area of the faceplate being energized. The two pairs of triads define two mutually perpendicular lines which bisect each other.
In the manufacture of a CRT, it is conventional to form a faceplate sub-assembly and a funnel sub-assembly and secure them together, using the alignment projections to establish orientation, and then fit a tension band around the faceplate/funnel assembly at a location close to the joint between the faceplate sub-assembly and the funnel sub-assembly. After the CRT has been assembled, the yoke is positioned on the neck of the CRT and is electrically driven to deflect the point of incidence of the electron beams over the inner surface of the faceplate in a raster pattern. The electron gun structure is energized so that a cross-like image is formed on the faceplate of the CRT. The cross is formed by the central line of the raster and the central portion of each other line of the raster. The orientation of the yoke about the neck of the CRT is adjusted to bring the cross-like image into registration with the above-mentioned mutually perpendicular lines, and the yoke is then fixed in position.
The tension band carries mounting lugs that project from the tension band at the four corners of the faceplate, and these lugs are formed with holes that fit over threaded mounting studs of the support structure in which the CRT is mounted. Washers and nuts are then fitted over the studs. The holes are oversized with respect to the studs, permitting adjustment of the position of the CRT relative to the support structure. When the CRT is in the desired position, the nuts on the studs are tightened, and the washers engage the mounting lugs and clamp the CRT in position.
The support structure generally includes elements that define the orientation in which the support structure will be used. For example, in the case of an enclosure, the structure has a front wall that is formed with a generally rectangular opening, and when the CRT is mounted in the enclosure a central display area of the faceplate can be viewed through that opening. The opening has two mutually perpendicular axes of symmetry that are respectively vertical and horizontal when the enclosure is positioned on a horizontal support surface. It is normally desired that the cross-like image be in registration with the axes of symmetry of the opening. The lines of the raster will then be horizontal when the CRT is positioned in the support structure and the support structure is oriented for use.
Automatic equipment that is used for adjusting the position of the CRT relative to its support structure in order to bring the raster lines to a horizontal orientation prior to tightening the nuts on the studs is very complex and expensive.